Single photon computerized tomography (SPECT) imaging is an important tool for assessing brain perfusion. This study aims to establish a new quantified approach to SPECT using cocaine-induced changes in cerebral blood flow (CBF) as a model. Establishing this new SPECT technique will improve the management of brain ischemia due to cocaine and other pharmacological or disease processes. It also will characterize and localize cocaine's effects on CBF in cocaine abusers during drug-taking to understand the actions of cocaine in the brain.This is the second year of this SPECT project which has proceeded according to plan. Nine subjects completed all parts of the protocol. Publications are currently in preparation and there is a new NIH application awaiting review for funding to extend this work for a further 5 years. Current arrangements with the CRC have added greatly to patient safety and the scientific conduct of this experiment.